Transcript Population Ecology - El Paso High School

Population Ecology
Populations

A population is a
group of
individuals of the
same species that
live in the same
area
Population Ecology: Vocabulary

Density:
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The number of individuals per unit
area/volume
Example: 47 elephants/km2
Dispersion:

The pattern of spacing among
individuals in a population
Clumped
 Uniform
 Random
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Uniform
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Environmental
conditions are
uniform
Causes
COMPETITION or
antagonism
between
organisms
Clumping
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Most common
Reproductive
patterns favor
clumping
Social behaviors
lead to clumping
Optimal density is
usually
intermediate
(medium)
Random
No
competition
 No tendency
to
group/clump
 Conditions are
uniform
 Rarely
happens!

Factors That Influence Population Size

There are 3 major factors that influence
population size:
1. the number of births
2. the number of deaths
3. the number of individuals that enter or
leave a population
- immigration:
individuals entering an existing population
- emigration:
individuals leaving an existing population
Reproductive Episodes
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Clutch size:

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Number of offspring produced at each
reproductive episode
Semelparity

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A life history in which an organism spends
most of its energy in growth and development,
expend their energy in one large reproductive
effort, and then die
Many insects, annual plants, salmon, etc.
Reproductive Episodes

Iteroparity
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A life history pattern in which
organisms produce fewer offspring at a
time over a span of many seasons
Example: humans, panda bears, etc.
Estimating Population Size
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The mark-recapture method can be
used to estimate the size of a
population
Capture, mark, release
Recapture and count
Equation:
N = Number marked x Total catch 2nd time
Number of marked recaptures
Patterns of Population Growth

Exponential Growth:
 Occurs in ideal
conditions with
unlimited resources
 J shaped curve
 Book example:
 1 bacterium
(reproducing every
20 minutes) could
produce enough
bacteria to form a 1foot layer over the
entire surface of the
Earth in a day
Patterns of Population Growth
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Exponential growth
cannot continue
indefinitely
It is characteristic of
populations who are
entering a new
environment OR
those whose
numbers are
rebounding from a
catastrophic events
r- strategists
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Grow exponentially when environmental
conditions allow; when conditions
worsen, population size plummets.
Short life span
Reproduce early in life
Many offspring/large clutch size
Usually small in size
Little or no parental care
Bacteria, some plants, insects
Patterns of Population Growth

Logistic Growth:
 Pattern of population
growth which takes
into account the
effect of population
density on population
growth
 Occurs when
resources become
more scarce
 Characterized by an
S-shaped curve
Patterns of Population Growth
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Carrying capacity (K):

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The maximum number of individuals that a
particular environment can support over a long
period of time
Determined by such limiting factors as crowding
and food resources
Graph levels off at carrying capacity
K-selected populations (equilibrial
populations) live near or at the carrying
capacity
K-strategists
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Density stays near carrying
capacity.
Large, slow growing organisms
Small population sizes
Long life span; slow maturation
Few young/small clutch size
Reproduce late in life
Parental care
Most large mammals; endangered
species
Carrying Capacity
Boom-and-Bust Cycles
Limiting Factors
 There
are a number of factors
that limit the size of
populations:
Density-dependent limiting
factors
 Density-independent limiting
factors

Density-Dependent Limiting Factors
 The
effect of density-dependent
limiting factors intensifies as
the population increases

Intraspecific competition
 Food,
space, etc.
Predation
 Disease (if caused by
pathogen/contagious)

Density-Independent Limiting Factors
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The occurrence and severity of
density-independent limiting
factors are unrelated to population
size
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Climate
Disease (if not caused by pathogen/not
contagious)
Pollution
The Interaction of Limiting Factors
 Density-dependent
and densityindependent limiting factors
often work together to regulate
the size of a population

Deer in snowy winter
 Starve
from lack of food (DDLF)
 Severity of winter/depth of snow
determines access to food (DILF)
Survivorship Curves
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Type I- live to old age
& die (most large
mammals)
Type II- constant
mortality rate (rodents,
lizards, hydra)
Type III- high mortality
at young age, but if
they survive they live a
long life.
Age-Structure Diagrams
Human Population Growth
Human Population Growth


The human population has been
increasing exponentially since
approximately 1650
http://www.pbs.org/wgbh/nova/wor
ldbalance/numbers.html
Human Population Growth
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Implications of exponential human
population growth:
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Lack of food supplies
Lack of space
Lack of natural resources (metals, fossil fuels, etc)
Lack of sites for waste disposal
Ecologists cannot agree on a carrying
capacity for Earth

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Are we going to reach carrying capacity
through individual choices and/or government
programs?
OR
Is Earth’s population going to “level off” as a
result of mass deaths?